Emergency service calls in North America are originated by dialing “9-1-1.” Other parts of the world may use some other abbreviated string of dialable digits such as “6-1-1” in Mexico; all share the intent to provide the caller with an easy way to call for help with an easy to remember number. These calls are routed to a local Public Service Answering Point (PSAP) where an emergency response may be initiated (police, fire department, road repair, ambulance, etc.) while the caller is kept on the phone. If the call is somehow disconnected or dropped before the emergency is completely reported or the responder arrives, the PSAP may call back the originator using a call back number provided through its databases.
For example, the call record for a 911 call originated through a wired communication network may include Automatic Line Identification (ANI) or the telephone number of the access line from which the call originated. With the introduction of local number portability (LNP) to the public telephone network, a subscriber may switch their telephone service from a landline service provider (LSP) to a wireless service provider (WSP) and port their directory number (DN) (e.g., a phone number) from the LSP to the WSP. During that transitional time period between when a number is ported to and activated by a WSP and deactivated by a LSP (hours to days), emergency service calls may still be originated from the old wired phone as well as the new mobile phone. However, according to current standards, the same DN will be presented to the PSAP as the callback number for both phones.
Since the DN presented to the PSAP as a callback number has been ported to a WSP, a callback from the PSAP will likely be routed through the WSP to a mobile station (MS). This will happen even if the initial emergency call originated at the wired phone. Namely, there is no unique callback number to the wired phone during this transitional time period.